1. Field of the Invention
This invention relates to nonionic emulsifiers obtained by acid-catalyzed acetalization of sugars with excess fatty alcohols, the conversion being limited to 60 to 90% of the theoretical, neutralization and filtration with back-mixing, to a process for their production and to their use for the production of surface-active preparations.
2. Discussion of Related Art
Alkyl oligoglycosides and, more particularly, alkyl oligoglucosides are nonionic surfactants which are acquiring increasing significance by virtue of their excellent detergent properties and their high ecotoxicological compatibility. They are produced from sugars or starch degradation products which are normally acetalized in the presence of acidic catalysts. For reasons associated with the law of mass action, it is advisable continuously to remove the water of condensation from the reaction equilibrium and to use one component, usually the less expensive fatty alcohol, in an adequate excess. On completion of the reaction, the acidic catalyst is neutralized, for example with sodium hydroxide and/or magnesium oxide, and the excess fatty alcohol is distilled off, usually to a residual content of &lt;1% by weight. To obtain light-colored products, it has proved to be necessary in this regard to limit the percentage content of unreacted sugar to 1% by weight and preferably to 0.5% by weight or, in other words, to aim at a substantially quantitative conversion.
In addition to alkyl oligoglycosides, surfactant compounds containing the corresponding fatty alcohol as second component have proved to be particularly skin-compatible emulsifiers in the field of cosmetics. The preparation of such mixtures is comparatively simple and, in general, merely involves simply leaving the fatty alcohol present in excess during the production of the alkyl oligoglycosides in the product.
Thus, the use of a mixture containing 60 to 90% by weight of a C.sub.12-22 fatty alcohol, 10 to 90% by weight of an alkyl oligoglycoside of corresponding chain length and optionally 0.5 to 5% by weight of a glycoside for the production of emulsions is known, for example, from WO 92/06778 (Seppic).
In addition, o/w emulsions containing 5 to 30% by weight of a water-insoluble oil, 2 to 15% by weight of a C.sub.18-22 alkyl oligoglucoside, 2 to 20% by weight of a fatty acid partial glyceride and optionally linear saturated fatty alcohols are claimed in DE-A1 40 33 928 (Henkel).
It is known even from the production of "pure" alkyl oligoglycosides that they are heavily discolored after removal of the excess fatty alcohol and have to be treated with bleaching agents. The same problems affect--albeit not to the same extent--compounds which, in addition to the alkyl and/or alkenyl oligoglycosides, contain the excess fatty alcohol as second component. In this case, too, bleaching with a peroxide is generally necessary for the production of light-colored products marketable for cosmetic purposes.
Another problem which is also known from the production of alkyl oligoglycosides are the long reaction times and the resulting correspondingly long reactor possession times. As already mentioned, it has been found to be necessary to minimize the content of free unreacted glucose in the reaction mixture because it can decompose during the distillation step and can give rise to color-producing components. In addition, significant amounts of unwanted higher oligomers (degree of condensation&gt;2) up to and including polyglucose can be formed.
However, since removal of the fatty alcohol by distillation is expressly not included in the production of the nonionic emulsifiers according to the invention, free fatty alcohol being intended to remain in the mixture, applicants have attempted to limit the conversion and to terminate the reaction after a certain time. Although comparatively light-colored products with a smaller content of higher oligomers are obtained in this way, they still do not meet the high quality requirements which cosmetic starting materials are expected to satisfy.
Accordingly, the problem addressed by the present invention was to provide nonionic emulsifiers containing alkyl and/or alkenyl oligoglycosides and fatty alcohols which would be distinguished by high color quality and a low percentage content of polysugars. At the same time, the reaction times would be significantly shortened.